[ESLint] Fix violations when enabling curly rule in eslint.

tracing/tracing/ui/analysis/single_thread_slice_sub_view.html

Index: tracing/tracing/ui/analysis/single_thread_slice_sub_view.html
diff --git a/tracing/tracing/ui/analysis/single_thread_slice_sub_view.html b/tracing/tracing/ui/analysis/single_thread_slice_sub_view.html
index 940c5b0ff1d3ee52b6f811db8eb769c9457ff267..720fdfeb65a4fb169e383f8231d8c43fc494dde7 100644
--- a/tracing/tracing/ui/analysis/single_thread_slice_sub_view.html
+++ b/tracing/tracing/ui/analysis/single_thread_slice_sub_view.html
@@ -43,10 +43,11 @@ Polymer({
   set selection(selection) {
     this.$.content.selection = selection;
     this.$.relatedEvents.setRelatedEvents(selection);
-    if (this.$.relatedEvents.hasRelatedEvents())
+    if (this.$.relatedEvents.hasRelatedEvents()) {
       this.$.relatedEvents.style.display = '';
-    else
+    } else {
       this.$.relatedEvents.style.display = 'none';
+    }
   }
 });